linux-kernel - Re: [PATCH 4/4] sched: bias to target cpu load to reduce task moving

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Message-ID: <20131217153809.GP21999@twins.programming.kicks-ass.net>
Date:	Tue, 17 Dec 2013 16:38:09 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	Alex Shi <alex.shi@...aro.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"fweisbec@...il.com" <fweisbec@...il.com>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	"fenghua.yu@...el.com" <fenghua.yu@...el.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"arjan@...ux.intel.com" <arjan@...ux.intel.com>,
	"pjt@...gle.com" <pjt@...gle.com>,
	"fengguang.wu@...el.com" <fengguang.wu@...el.com>,
	"james.hogan@...tec.com" <james.hogan@...tec.com>,
	"jason.low2@...com" <jason.low2@...com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"hanjun.guo@...aro.org" <hanjun.guo@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] sched: bias to target cpu load to reduce task moving

On Tue, Dec 17, 2013 at 02:10:12PM +0000, Morten Rasmussen wrote:
> > @@ -4135,7 +4141,7 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, int this_cpu)
> >  			if (local_group)
> >  				load = source_load(i);
> >  			else
> > -				load = target_load(i);
> > +				load = target_load(i, sd->imbalance_pct);
> 
> Don't you apply imbalance_pct twice here? Later on in
> find_idlest_group() you have:
> 
> 	if (!idlest || 100*this_load < imbalance*min_load)
> 		return NULL;
> 
> where min_load comes from target_load().

Yes! exactly! this doesn't make any sense.
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